The present invention relates to optical signal conversion and amplification. In particular, it improves on the devices and methods of U.S. Pat. No. 5,604,628 issued Feb. 18, 1997, U.S. Pat. No. 5,742,045 issued Apr. 21, 1998, and U.S. Pat. No. 5,748,653 issued May 5, 1998, the disclosures of which are hereby incorporated by reference. The present invention improves the Lasers with Optical Gain Control ("LOGiC") devices and methods of these patents by providing a mechanism for signal amplification and conversion of a frequency-modulated ("FM"), a wavelength-multiplexed ("WM"), or an amplitude-modulated ("AM") optical signal into an amplified amplitude-modulated optical signal.
The LOGiC devices offer the possibility of integrating all-optical high-speed communications and signal processing. These devices can route signals, exercise logic functions, and filter spontaneous emission. A LOGiC device typically comprises a semiconductor main laser with a control beam that enters the side of the laser cavity at right angles (see FIG. 1 for a block diagram). The main laser can be an in-plane laser (IPL), a vertical cavity laser (VCSEL), or an electrically/optically-pumped semiconductor amplifier. The control beam can originate from a monolithically integrated optical amplifier or semiconductor laser or from a fiber/waveguide that is butt-coupled to the side of the main laser. In operation, increasing control-beam power P.sub.c (with angular frequency .omega..sub.c) causes output-beam power P (with angular frequency .omega.) to decrease. Other optical modulation is possible for fiber lasers that use DBR mirrors and two longitudinal modes.
Although a number of LOGiC devices have been developed for signal routing, optical filtering, and Boolean logic, these devices do not have optical gain--defined by ##EQU1##
is less than one for devices of the prior art. Optical gain G.sub.opt &gt;1 is required to regenerate, amplify, and condition optical signals and to cascade LOGiC devices in multi-element circuits. When the optical gain is greater than one (G.sub.opt &gt;&gt;1), small variations in an input signal P.sub.c result in large changes of an output signal P, hence amplification.
In addition, the LOGiC devices of the prior art do not explicitly address the possibility of optical FM demodulation. Demodulation and wavelength conversion are important for optical signal routers and communications systems. FM communications links are generally chosen over AM links when low-noise characteristics are important. However, there is no single, integrable device that can convert a FM signal into an AM signal, as is typical of a FM discriminator in communications equipment.
Therefore the LOGiC devices of the prior art can be improved by adding mechanisms for optical gain, demodulation, and wavelength conversion.